The Caribbean plate: Pulled, pushed, or dragged?

Mechanical coupling between the lithosphere and the asthenosphere remains a controversial topic in the geosciences. Beneath the Caribbean plate, shear wave splitting measurements indicate EW strain in the asthenosphere, which can be interpreted as mantle flow driving or resisting motion of the overlying lithosphere. Here, we constrain the average shear traction on the base of the Caribbean plate by balancing all torques. These torques result from body forces that act on the Caribbean (slab pull, ridge push, lateral density variations), from plate boundary friction and from basal shear tractions. We obtain a range of physically realistic torque solutions, which we examine further by computing the corresponding stresses and rotations within the Caribbean plate for comparison with observations. The deformation field for the Caribbean is particularly sensitive to the amount of friction on intraplate faults. Representative models have a good fit with observations and are characterized by (1) a near-zero basal shear traction (<= 0.3 MPa), (2) (lithosphere-averaged) plate boundary friction <= 10 MPa, (3) local forces due to indenters and trench pull, (4) a net pull by the Caribbean slab and (5) intraplate fault shear stresses on the order of tens of megapascals. We conclude that the mechanical coupling of the Caribbean plate to the underlying asthenosphere is small.